This detection rule targets suspicious HTML attachments that exhibit excessive string concatenation, often linked with HTML smuggling techniques. Such HTML files typically try to obfuscate their content to bypass security measures. The rule specifically checks for email recipients within the attachment, assesses the file type and size, and looks for multiple instances of concatenation characters, indicating an attempt to obscure the true nature of the content. Moreover, red flags are raised if typical HTML smuggling indicators such as 'window.location.href' or 'createObjectURL' appear in the raw HTML content. This detection is critical due to its association with credential phishing attacks, where attackers use these tactics to trick users into divulging sensitive information.